This invention relates to goniometers, namely a rotational positioner whose center of rotation is located outside the physical boundaries of the device. It is used for partial rotation of parts too large for the thru hole of a full rotational stage.
Linear micropositioners are known e.g. from U.S. Pat. No. 3,046,006 and arcuate rolling bearings in which balls, controlled by cages, roll in opposed arcuate gothic arch shaped tracks allegedly providing a four-point contact surface are known e.g. from U.S. Pat. No. H539. Goniometers are also known with current designs typically comprising stages, mounted for limited rotation, controlled by i.e. arcuate dovetail mating grooves or arcuate cross-roller arrangements with cooperating V-grooves. These arrangements do not provide negligible eccentricity coupled with smooth sensitive action as is required i.e. for fiber optic alignment.
An object of the present invention is to provide a number of designs of goniometers which overcome shortcomings of current designs.
The design is an improvement over the current designs where shorter rotational travels (minor adjustments, 3-20xc2x0) and smooth sensitive and repeatable action are required, but exact long range eccentricity and load capacity are not, such as in fiberoptic alignment. The present invention provides goniometers which are considerably cheaper, and possibly better than using precision roller ways. It employs three or four bearing balls, two riding in counter-v-grooves at least one of which is a V-groove opposed to a non-constraining flat surface, to give complete kinematic stability in every aspect except rotation.
The design with the three ball bearings is the simplest and this affords a three-point contact for low load requirements.
The four-ball version allows perfect four-point contact, which is not achievable in the linear stage as patented (see U.S. Pat. No. 3,046,006). This is because the rotor is free to rotate on its axis normal to the axis of rotation of the device until all four points are touched simultaneously.
The invention provides a goniometer comprising a rotor and a support base having therebetween four balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the four balls being constrained to be spaced apart in at least two dimensions with at least one ball thereof being supported to adjust its position to ensure a four point spaced apart support contact between the rotor and the support base.
The invention also provides a goniometer comprising a rotor and a support base having therebetween three balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the three balls being constrained to be spaced apart in at least two dimensions to ensure a three point spaced contact with the rotor and the support base.
A possible further version employs pre-fabricated bearing races, cut into sections for partial rotation, as separate parts attached to receiving areas in the goniometer body, rather than machining them right in. This allows the design to eliminate the third groove pair, while the second groove pair manages its former operation by having the attributes of both groove pairs built into one.
Another embodiment, using the four ball system, is one in which the cylinder pair is xe2x80x9cvery long as compared to the diameter, and also in 2 sections. This would allow a very lightweight off-axis tilt table.
According to the invention there is provided a goniometer comprising a rotor and a support base having therebetween at least three balls constrained to at least two arcuate paths to allow rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the balls being constrained to be spaced apart in at least two dimensions arranged in said arcuate paths to ensure at least a three point spaced contact of the rotor with the support base.
Preferably there are two parallel spaced apart said arcuate grooves, at least one said arcuate groove being formed by facing cooperating V-grooves, one defined by the rotor and the other defined by the support base, retaining two said balls in spaced apart relationship in laterally constrained contact with said V-grooves.
Four balls may be provided, between the rotor and the support base, constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions with at least one ball thereof being supported to allow self adjustment of its position to ensure a four point spaced apart support contact between the rotor and the support base; preferably there are first, second and third said arcuate paths, the first and second said arcuate paths being spaced apart and each defined by an arcuate V-groove defined one of the rotor and the support base and an arcuate flat surface defined by the other of the rotor and support base and the third arcuate path being defined by facing cooperating arcuate V-grooves located adjacent said first arcuate path, two said balls being disposed and constrained in spaced relationship in the second said arcuate path in contact with the rotor and the support base, a third said ball being disposed and constrained in said first arcuate path in contact with the rotor and support base and the fourth said ball being disposed in said third arcuate path wherein the said fourth ball is free to move along said third arcuate path to allow said self adjustment to a position to ensure said four point spaced apart support contact.
In another embodiment, four balls between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths each defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, two said balls being disposed in spaced relationship in each arcuate path in contact with the rotor and the support base arranged to ensure a four point spaced apart support contact between the rotor and the support base.
In another embodiment, four balls, between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the four balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths, the first said arcuate path being defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, two said balls being disposed in spaced relationship in each arcuate path in contact with the rotor and the support base with the two balls disposed in the second arcuate path being constrained by opposed V-grooves forming the second arcuate path, thereby to ensure a four point spaced apart support contact between the rotor and the support base. Longitudinal movement of the rotor on the support base parallel to axis of rotation may be controlled by a lateral support arrangement.
In another embodiment, a rotor and a support base have therebetween three balls constrained to follow arcuate paths to provide rotation of the rotor, relative to the support base, about an axis of rotation external to the rotor, the three balls being constrained to be spaced apart in at least two dimensions to ensure a three point spaced contact with the rotor and the support base.
In a preferred three ball embodiment, three balls, between the rotor and the support base, are constrained to follow arcuate paths to allow said rotation of the rotor, relative to the support base, the three balls being constrained to be spaced apart in at least two dimensions wherein there are first and second said spaced apart arcuate paths, the first said arcuate path being defined by an arcuate V-groove defined by one of the rotor and support base and a non-constraining arcuate flat surface defined by the other of the rotor and support base, one said ball being disposed in the first said arcuate path in contact with the rotor and the support base and two balls being disposed spaced apart in the second arcuate path constrained by opposed V-grooves forming the second arcuate path, thereby to ensure a three point spaced apart support contact between the rotor and the support base.
In yet another four ball embodiment the goniometer has a rotor and support base each defining a single arcuate surface which are complimentary and together define an arcuate space with four balls therein, the four balls being constrained to at least two arcuate paths by a cage common to all four balls.